[Sound clip] That's the future sound filling city streets. If President Obama has his way there will be one million electric vehicles on the road by 2015. This week the National Highway Traffic Safety Administration started a process to determine what should be done to make it easier for pedestrians and others who share the road to detect these quiet cars.

[clip 1] That electronic [sound clip] is one of several alternatives if the NHTSA decides to require these cars to add sounds. Here's another [sound clip].

The goal is to give an audio cue, not unlike the beeping associated with the backing up of large trucks. Why? Well, a study led by psychologist Lawrence Rosenblum of the University of California, Riverside, found that blindfolded test subjects could hear an internal combustion engine 36 feet away but didn't hear a hybrid until it was a mere 11 feet away.

That left scant few seconds to react before the hybrid reached them. And that's not safe. Which is why the electric or hybrid cars of the future may sound so, well, futuristic.—David Biello